A human rights monitoring group says that fighters with the Islamic State (IS) extremist group have killed dozens of people while attacking government-held neighborhoods in the city of Deir al-Zor in eastern Syria.

The Britain-based Syrian Observatory for Human Rights said on January 16 that IS fighters killed pro-government fighters and their families as they attacked two neighborhoods in the disputed city.

The IS militant group is in control of most of the eastern Deir al-Zor province while the government holds parts of the city of the same name, including a military airport.

Deir al-Zor province links Islamic State's de facto capital in Raqqa with territory controlled by the group in Iraq.